1. Technical Field of the Invention
This invention relates generally to energy monitoring systems and more specifically to electrical power monitors as used in residential energy management systems.
2. Background Art
There is a broad growing interest in energy conservation. Reducing residential electrical consumption is a priority for national, state, and local governments, for utilities, and for consumers. It is especially important to reduce electrical consumption during peak load periods, typically in the afternoon on hot days. It is generally accepted that consumers are more likely to change their behavior if they are made aware of where, when, and how they use electricity in their household and how much it costs. A power monitoring system provides this information.
The simplest monitor displays the present rate of power use. Its function is similar to the power meter used by the utility company for billing, but it displays the information in a format and location that this more convenient for consumers. The power can be displayed in units of electricity (kilowatts) or in units of cost ($x.xx per hour). The display can be portable or located in a convenient place in the home. This type of monitor can make the consumer aware of the total cost of the electricity used by the household at the present time, and the power can be accumulated to show the total power used during a period of time and its cost. U.S. Pat. No. 7,174,260 issued Feb. 6, 2007 to Tuff, et al. describes such power monitor. It uses an optical sensor to monitor the power meter wheel as it turns and processes this information into rate of power use and cost. This information is wirelessly sent to a display device located in the residence. The device also accumulates the total power used during a period of time and its cost.
Other monitors extract information about the status of an electrical device by analyzing the amount of power used as a function of time. A power measuring device is used for each monitored electrical device and the power measurements are communicated to a central processor. Analysis of the changes in power use can determine the status of the device which is then displayed. U.S. Pat. No. 6,906,617 issued Jun. 14, 2005 to Van der Meulen describes such a system. The disadvantage of this approach is that a separate complex power monitor is used for each electrical device.
More sophisticate monitoring systems record the energy used over a period of time and processes and/or displays the information to make it more useful to the consumer. For example a graph of power use versus time can show the consumer how power use varies with household activity. As another example, the consumer might specify a start time and an end time, and the monitor might respond with the cost of power used during this period. U.S. Pat. No. 7,246,014 issued Jul. 17, 2007 to Forth, et al. describes such a system and describes several ways to display the information.
An increasing number of utilities are charging different rates for power depending on the time of day, day of week, or based on the total electricity used during the billing period. Some monitoring systems integrate this information with the measured power to provide the consumer more accurate and useful information that might encourage them to reduce energy consumption and/or change when they use power. For example, they might chose to reduce the amount of air conditioning used when electricity is expensive and to run their pool pump or do laundry at times when electricity is less expensive. U.S. Pat. No. 5,289,362 issued Feb. 22, 1994 to Liebl, et al. describes a system where a variation in the cost of electricity alters the settings for HVAC equipment.
While knowing the power and total power used by a household has value, there is more value in knowing the power and total power used by individual electrical devices. This information enables the consumer to make informed decisions about altering usage patterns and/or upgrading to new and/or higher efficiency devices. There exist power monitors that can be connected to an individual power circuits, individual outlets, and to individual devices. The disadvantage of this approach is an additional power sensor and a method of reporting its measurements are needed for each device monitored.
What is missing in the prior art for power monitors is a practical and economical method of using a single central power monitor to provide detailed information about the power and total power used by multiple individual electrical devices.